An electric field was introduced into the thermal oxidation synthesis of CuO nanowires (NWs) by heating Cu foils at 400 °C under ambient conditions using a hotplate. The morphology and crystal structure of the NWs on both sides of the foils synthesized under different electric field intensities and directions were characterized. The results indicated that adding an electric field increases the length and density of the CuO NWs. Particularly, the electric field can promote the growth of the NWs with the growing direction parallel to the electric field through accelerating the diffusion of Cu ions. Interestingly, a downward electric field and an upward temperature gradient change the growth direction of NWs on the bottom surface of the Cu foils. Besides, adding a downward electric field can increase the yield of CuO NWs with large aspect ratio, as they can grow on both sides of the Cu foil. The field emission properties of CuO NWs obtained under different electric fields indicated that these nanowire arrays could be used as the cathode of field emission displays.
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